1. Convert to string

const input = 123;

console.log(input + ''); // '123'
console.log(String(input)); // '123'
console.log(input.toString()); // '123'


2. Convert to number

const input = '123';

console.log(+input); // 123
console.log(Number(input)); // 123
console.log(parseInt(input)); // 123


3. Convert to boolean

const input = 1;

// Solution 1 - Use double-exclamation (!!) to convert to boolean
console.log(!!input); // true

// Solution 2 - Pass the value to Boolean()
console.log(Boolean(input)); // true


4. Problem with the string 'false'

const value = 'false';
console.log(Boolean(value)); // true
console.log(!!value); // true

// The best way to check would be,
console.log(value === 'false');

5. null vs undefined

null is a value, whereas undefined is not.null is like an empty box, and undefined is no box at all.
ex.,

const fn = (x = 'default value') => console.log(x);

fn(undefined); // default value
fn(); // default value

fn(null); // null


When null is passed, the default value is not taken, whereas when undefined or nothing is passed the default value is taken.

6. Truthy and Falsy values

Falsy values - false, 0, "" (empty string), null, undefined, & NaN.

Truthy values - "false", "0", {} (empty object), & [] (empty array)

7. What changes can be made with const

const is used when the value does not change. ex,

const name = 'Codedrops';
name = 'Codedrops.tech'; // Error

const list = [];
list = [1]; // Error

const obj = {};
obj = { name: 'Codedrops' }; // Error


But it can be used to update value in previously assigned arrays/objects references

const list = [];
list.push(1); // Works
list[0] = 2; // Works

const obj = {};
obj['name'] = 'Codedrops'; // Works

8. Difference between double equal and triple equal

// Double equal - Converts both the operands to the same type and then compares
console.log(0 == '0'); // true

// Triple equal - Does not convert to same type
console.log(0 === '0'); // false


9. Better way to accept arguments

function downloadData(url, resourceId, searchText, pageNo, limit) {}

downloadData(...); // need to remember the order


Simpler way to do this-

function downloadData(
{ url, resourceId, searchText, pageNo, limit } = {}
) {}

downloadData(
{ resourceId: 2, url: "/posts", searchText: "programming" }
);

10. Rewriting normal function as arrow function

const func = function() {
console.log('a');
return 5;
};
func();


can be rewritten as

const func = () => (console.log('a'), 5);
func();

11. Return an object/expression from arrow function

const getState = (name) => ({name, message: 'Hi'});


12. Convert a set to an array

const set = new Set([1, 2, 1, 4, 5, 6, 7, 1, 2, 4]);
console.log(set); // Set(6) {1, 2, 4, 5, 6, 7}

set.map((num) => num * num); // TypeError: set.map is not a function


To convert to an array

const arr = [...set];


13. Check if a value is an arr

const arr = [1, 2, 3];
console.log(typeof arr); // object
console.log(Array.isArray(arr)); // true


14. Object keys are stored in insertion order

const obj = {
name: "Human",
age: 0,
address: "Earth",
profession: "Coder",
};

console.log(Object.keys(obj)); // name, age, address, profession


Objects maintain the order in which the keys were created.

15. Nullish coalescing operator

const height = 0;

console.log(height || 100); // 100
console.log(height ?? 100); // 0


Nullish coalescing operator (??) returns the right-hand side value only if the left-hand side value is undefined or null

16. map()

It is a utility function which helps in applying a function on every element of the array.
It returns a new array, which contains the values returned from that applied function. ex.,

const numList = [1, 2, 3];

const square = (num) => {
return num * num
}

const squares = numList.map(square);

console.log(squares); // [1, 4, 9]


Here, the function square is applied to every element. i.e., 1, 2, 3.

The returned value of that function is returned as the new element value.

17. try..catch..finally - Real example

const getData = async () => {
try {
setLoading(true);
const response = await fetch(
"https://jsonplaceholder.typicode.com/posts"
);
// if error occurs here, then all the statements
//in the try block below this wont run.
// Hence cannot turn off loading here.
const data = await response.json();
setData(data);
} catch (error) {
console.log(error);
setToastMessage(error);
} finally {
setLoading(false); // Turn off loading irrespective of the status.
}
};

getData();

18. Destructuring

const response = {
msg: "success",
tags: ["programming", "javascript", "computer"],
body: {
count: 5
},
};

const {
body: {
count,
unknownProperty = 'test'
},
} = response;

console.log(count, unknownProperty); // 5 'test'


Thanks for reading 💙